Necrotizing Soft Tissue Infections - Complicated Skin Infections


Indications for Testing

  • Appropriate clinical presentation in addition to a high level of suspicion for the disease

Laboratory Testing

  • Simple infections – abscesses, furuncles, carbuncles
    • Gram stain of aspirates or tissue biopsies – may not be as helpful as culture, depending on organism involved and quality of specimen
    • Cultures of tissue, wound
  • More complicated infections (fever, tachycardia, immunocompromised patients)
    • CBC – elevated white cell count >15,000/mm3 with neutrophil predominance (left shift) frequently noted
    • Cultures of tissue, wound crucial
    • Blood cultures – infrequently positive but helpful for organism identification
    • C-reactive protein
    • Use of Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score – ≥6 points has positive predictive value of 92% and negative predictive value of 96% for diagnosis of necrotizing fasciitis
    • Laboratory Risk Indicator for Necrotizing Fasciitis

      Laboratory Risk Indicator 
      for Necrotizing Fasciitis

      Variable, Units


      C-reactive protein, mg/L  





      Total white cell count, per mm3







      Hemoglobin, g/dL







      Sodium, mmol/L





      Creatinine, µmol/L





      Glucose, mmol/L





      Maximum score is 13. 
      A score of ≥6 should raise the suspicion of necrotizing fasciitis. 
      A score of ≥8 is strongly predictive of this disease.

  • If above studies do not confirm necrotizing fasciitis, surgical exploration of the site may confirm the disease

Imaging Studies

  • X-ray – subcutaneous air in tissue noted in about 25% of patients
    • May reveal foreign body in infected wounds
  • US/CT/MRI – choose imaging study based on suspected location of infection and usefulness of study for site infected
    • Imaging frequently used for localized drainage of identified site

Differential Diagnosis

Clinical Background

Aggressive soft tissue infections can cause extensive local tissue damage as well as systemic toxicity. These infections require prompt recognition in order to prevent severe morbidity and mortality.


  • Incidence – 4/100,000
  • Age – usually occurs in older patients
  • Sex – M:F, equal 
    • Exception in Vibrio vulnificus, M>F
  • Transmission – skin entry via break in dermis (usual route)


  • Gangrene
  • Necrotizing fasciitis/cellulitis
  • Myositis/myonecrosis
  • Complicated/deep abscesses
  • Infected burns/surgical wounds
  • Toxin-mediated – toxic shock syndrome, staphylococcal scalded skin syndrome


  • Single organism common in uncomplicated infections; polymicrobic/synergistic more prominent in complicated infections
    • Staphylococcus spp (including methicillin-resistant Staphylococcus aureus[MRSA]), enterococci, Pseudomonas aeruginosa, Streptococcus spp, Enterobacteriaceae, Bacteroides spp, Proteus spp, Clostridium spp
      • Most common – Staphylococcus aureus, Streptococcus spp
    • Aerobic and anaerobic organisms frequently found in combination

Risk Factors

Clinical Presentation

  • General symptoms
    • Skin – erythema, tense edema, vesicles or bullae, necrosis ulcers, crepitus, gray or discolored wound drainage, pain extending past margin of skin infection
    • Constitutional – fever, diaphoresis, delirium, tachycardia, tachypnea
    • Most common locations – extremities (50-55%), perineum/buttocks (20%), trunk (18-20%), head and neck (8-10%)
  • Clinical markers that may help differentiate necrotizing infection from localized infection include the following
    • Pain disproportionate to appearance of infection 
    • Crepitus
    • High fever
    • Rapidly spreading erythema
  • Organisms and clinical scenarios/presentations


    Common Clinical Scenario

    Most Common Underlying Comorbid Illnesses

    Clinical Presentation


    Group A
    Streptococcus species

    Skin abrasion, trauma, recent skin infection (herpes zoster, varicella-zoster, herpes simplex), human bite, intravenous/ subcutaneous drug abuse

    Diabetes, cancer, alcoholism, stasis dermatitis, eczema

    Intense erythema, edema and pain, lymphadenopathy, hemorrhagic and necrotic bullae, muscle myositis, erysipelas, impetigo; type II necrotizing fasciitis

    One of the two most common monomicrobial infectious agents

    Peptostreptococcus and gram-negative

    Colorectal or genitourinary disease; orofacial surgery, dental work

    Older patients

    Scrotal edema and perineal gangrene (Fournier gangrene), submandibular space (Ludwig angina)

    Usually found in association with other organisms

    Staphylococcus aureus

    Skin trauma, recent hospitalization or surgery, intravenous/ subcutaneous drug abuse

    Obesity, diabetes, immunocompromising condition, eczema, rheumatologic diseases

    Furuncles, local abscesses, diffuse macular erythroderma, pyomyositis, toxic shock syndrome, staphylococcal scalded skin syndrome

    One of the most common agents of soft tissue skin infections

    Polymicrobial – often beta hemolytic streptococci with S. aureus (including MRSA), S. epidermidis or gram-negative bacteria such as E. coli, Proteus mirabilis, Klebsiella pneumoniae

    Diabetic foot ulcer, recent surgery with purulent wound

    Diabetes, immunocompromising condition, vascular disease (particularly lower extremity disease)

    Moist gangrene with a foul odor, suppurative-necrotic ulcer surrounded by concentric zones of red cellulitis (Meleney gangrene), deeper abscess, type I necrotizing fasciitis

    Most common presentation (>50% of all necrotizing soft tissue infections)

    Pseudomonas species

    Bacteremia, moist skin infection, severe burn, recent hospitalization

    Immunocompromising condition, diabetes

    Hemorrhagic and necrotic bullae


    Vibrio vulnificus

    Exposure to raw or undercooked seafood or exposure to seawater

    Underlying liver disease, immunocompromising condition

    Hemorrhagic and necrotic bullae, ecchymoses

    Unusual in immunocompetent patients

    Clostridium perfringens

    Severe trauma with wound contamination, recent surgery, intravenous drug abuse


    Pale skin, edema, hemorrhagic and necrotic bullae, foul-smelling discharge, gas formation

    Usually found in association with local tissue injury

    Pasteurella multocida

    Cat or dog bite


    Erythema, edema, serosanguineous discharge, lymphadenitis, tenosynovitis

    Typically associated with animal bite

    Aspergillus, Mucor, Rhizopus

    Traumatic wounds or burns

    Immunocompromising condition

    Erythema, severe pain, hemorrhagic bullae

    Rarely occurs in immunocompetent patients

    Aeromonas hydrophila

    Exposure to fresh water, skin abrasion

    Usually none; sometimes an immunocompromising condition

    Erythema, bullae, necrosis, possible gas formation

    Unusual in immunocompetent patients


  • Initiate antibiotic therapy appropriate for polymicrobial infections; change therapy to match culture results
  • Aggressive wound care, including wide-area surgical debridement
    • Necrotizing wounds are commonly fatal if not treated within 72 hours


  • Vibrio – do not eat raw seafood; avoid exposing open wounds to seawater
  • Pasteurella – prophylaxis started at time of bite for serious bite wounds

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Help differentiate aggressive (systemic) infection from local infection

May not be elevated in spite of aggressive disease

Wound Culture and Gram Stain 0060132
Method: Stain/Culture/Identification

Identify organism causing infection

Anaerobe culture is NOT included with this order

Tissue Culture and Gram Stain 0060127
Method: Stain/Culture/Identification

Identify organism causing infection

Anaerobe culture is NOT included with this order

Blood Culture 0060102
Method: Continuous Monitoring Blood Culture/Identification

May be useful in patients with toxic appearance/presentation

Testing is limited to the University of Utah Health Sciences Center only

C-Reactive Protein 0050180
Method: Quantitative Immunoturbidimetry

Component of Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score

Electrolytes, Urine 0020498
Method: Quantitative Ion-Selective Electrode

Component of LRINEC score

Glucose, Plasma or Serum 0020024
Method: Quantitative Enzymatic

Component of LRINEC score

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Clostridium botulinum culture

ARUP recommends contacting your local or state health department in suspected botulism cases

If local and state officials are not available, the CDC can be contacted